Automatic + codes, product + order + shipping, same-line tags — Shopify's combination engine will apply the best permitted stack. If you never set combinesWith deliberately, you didn't prevent stacking. You randomized it.
The empty promo-code field doesn't just sit there. It sends confident shoppers off to hunt for a code — and many don't come back. Collapse it, auto-apply, and stop advertising a better price.
Who approved that 30% code, why, and what did it cost? If you can't answer in under a minute, you don't have discount governance — and regulators increasingly expect it.
Most winback is a flat discount to everyone who lapsed. Tier it by why they left, try non-price first, and measure 90-day full-price repeat — not opens.